Synthesis, Structure, and Characterization of a Novel Manganese(IV) Monomer, [Mn(IV)(Me(3)TACN)(OMe)(3)](PF(6)) (Me(3)TACN = N,N',N"-Trimethyl-1,4,7-triazacyclononane), and Its Activity toward Olefin Oxidation with Hydrogen Peroxide.

Abstract

A novel manganese(IV) monomer, [Mn(IV)(Me(3)TACN)(OMe)(3)](PF(6)), has been synthesized in methanol by the reaction of MnCl(2) with the ligand, N,N',N"-trimethyl-1,4,7-triazacyclononane (Me(3)TACN), in the presence of Na(2)O(2). The resulting product was isolated as the red/brown crystalline hexafluorophosphate salt. The compound crystallizes in the space group P2/c with the cell dimensions a = 15.652(2) Å, b = 8.740(1) Å, c = 15.208(2) Å, beta = 108.81(1) degrees, V = 1969.4(4) Å(3), and Z = 4. The structure was solved by the heavy-atom method and was refined by full-matrix least-squares techniques to a final value of R = 0.067 (R(w) = 0.097) based upon 3087 observations. The manganese atom in the molecule is six-coordinate in an N(3)O(3) ligand environment with the triazacyclononane facially coordinated. Pertinent average bond distances and angles are as follows: Mn-O, 1.797(5) Å; Mn-N, 2.116(5) Å; O-Mn-O, 97.8(2) degrees; N-Mn-N, 81.4(2) degrees; O-Mn-N, 167.8 degrees (2); O-Mn-N, 86.8(2) degrees; O-Mn-N, 92.8(2) degrees. The complex was further characterized by UV-vis and EPR spectroscopies, solution magnetic susceptibility measurements, FAB-MS, and electrochemistry. [Mn(IV)(Me(3)TACN)(OMe)(3)](PF(6)) was found to catalyze the oxidation of water-soluble olefins using hydrogen peroxide as the oxidant in an aqueous medium. The catalyzed rates of oxidation of these olefins indicate at least a 12-fold rate enhancement over oxidant alone. The unusual stability of the catalytic species was demonstrated by the repeated additions of substrate and oxidant while maintaining a constant catalytic rate of oxidation.